Ahhhh...much better

rFactor ships with single cpu support. To unleash all your horses, open the rFactor alias placed in your Home folder/Applications. Rt-click/Ctrl click it, open package contents, and open the Info.plist file. Look for the CrossoverHelper Command field, and double-click the string. Add a space and +fullproc to the end. The last bit should look like this: ...Programs/rFactor/rFactor" +fullproc
This cleans up many graphics issues, and overall gameplay is much smoother.
Boot Campers should also do this by rt-clicking the rFactor icon, clicking Properties, and entering as above to the Target field.